Semiconductor memory devices are used to store data, and may be classified as volatile memory devices and nonvolatile memory devices. Volatile memory devices lose stored data when power supply is interrupted, while nonvolatile memory devices do not.
Because nonvolatile memory devices typically can store data with relatively low power consumption, nonvolatile memory devices are commonly used as a storage medium for mobile devices. Examples of nonvolatile memory devices include flash memory devices and variable resistance memory devices.
Examples of variable resistance memory devices include ferroelectric RAMs (FRAMs) using ferroelectric capacitors, magnetic RAMs (MRAMs) using tunneling magneto-resistive (TMR) films, and phase change memory devices using chalcogenide alloys. Phase change memory devices may be fabricated using relatively simple manufacturing processes and can provide relatively large memory capacity at a relatively low cost.
Variable resistance memory devices may be affected by heat. For example, when a variable resistance memory device is exposed to a high temperature for a long time, stored data may be lost. This can reduce reliability of a memory system using such devices.